Image sensors are devices for converting one or two dimensional optical imformation (e.g., optical image) into an electrical signal. Image sensors may be classified into complementary metal-oxide-semiconductor (CMOS) image sensors and charge coupled devices (CCD) image sensors. CCD image sensors exhibit superior photo-sensitivity and noise properties as compared to CMOS image sensors. CCD image sensors, however, are disadvantageous in view of the difficulty obtaining high-integration and also due to its high power consumption. On the other hand, CMOS image sensors (CIS) are advantageous in that they involve simple processes, are suitability for highly integrated devices and exhibit low power consumption.
Accordingly, the recent rapid progress in semiconductor device fabrication techniques has brought about great improvement in CIS fabrication techniques and properties. As a result, active research is being made on CIS. In CIS research, sensitivity improvement is the most important reaserch subject. In order to enhance sensitivity, it is important to maximize light absorption while minimizing light loss. To realize sensitivity improvement, various factors including the shape of microlenses, the thicknesses of dielectrics and sensitivity of photodiodes must be taken into consideration.
Since general techniques employ color filters made of photoresist materials, they are disadvantages since metals to prevent optical loss cannot be directly deposited on the color filters. Accordingly, there is a limitation in improving sensitivity by isolating color filters from each other.